A. Field of the Invention
The present invention relates broadly to an internal drive mechanism in an air compressor and, more specifically, to a drive mechanism for use in a supercharger for an internal combustion engine or an air compressor of the type driven mechanically by the engine or other power source.
B. Discussion of the Prior Art
It is well known that in a supercharger or air compressor, increasing the volume of air charge delivered to the combustion chamber of an internal combustion engine will increase the output of the engine for a given displacement at a given engine speed. There are two basic types of superchargers, centrifugal and positive displacement. The centrifugal type is very efficient, providing the best ratio between unit dimensions and flow volume. The air compression in the centrifugal design is achieved using a scroll or scroll-shaped air chamber having a centrally located air inlet and an impeller rotatably disposed in the air inlet to draw in air and then the compress the air within the scroll. An air outlet connected to the combustion chamber delivers the compressed air to the engine. Centrifugal designs require high peripheral compressor-wheel or impeller velocities approaching or exceeding the speed of sound, which can be achieved with either an exhaust-driven direct-drive turbine compressor wheel combination, or a mechanical drive connected between the engine crankshaft and the input shaft of the supercharger. The overall speed ratio between the impeller and the crankshaft should be, practically, at least nine impeller rotations for every rotation of the crankshaft, and the outer external mechanical drive is usually limited to a step-up ratio of approximately three input shaft rotations for every rotation of the crankshaft. Thus a further internal step-up mechanism is desired to increase the impeller to three or four additional rotations for every rotation of the input shaft.
It is known in air compressors that a step-up ratio of 9 to 1 between power sources and the impeller is desirable. Presently this ratio has been attempted using external step-up drives only; however, such configurations result in relatively low speeds and low flow when compared to an air compressor with an internal step-up drive. Internal drives have in the past not been considered reliable for this intended use.
Previously known internal drive mechanisms have employed planetary traction drives, or gear drives. An example of an internal gear drive mechanism is disclosed in U.S. Pat. No. 5,224,459, issued to James Middlebrook. In general, traction drives or gear drives require lubrication, causing unwanted heat buildup, which thereby tends to reduce the density of the compressed air discharge. Planetary step-up ball and/or race drives require preloading of the mechanism to prevent slippage, due to the necessity of lubrication and traction to transmit rotational power. The preloading of these drives and the related lubrication causes further intrinsic heat buildup, thus further reducing the density of the compressed air discharge. Gear drives are undesirably noisy to operate, usually requiring hot engine oil to lubricate the gears and bearings, causing additional heat buildup, which also contributes to a reduction of the air density. In addition, the gear drives must be connected to the engine oil reserve, making them more difficult to install and maintain.
The general object of the present invention is to provide, in an air compressor or supercharger, an internal drive mechanism which, as compared to prior internal drive mechanisms, generates less heat, operates with greater efficiency, requires less energy to operate and facilitates installation on the engine or other power source.
A more specific object is to provide an internal drive mechanism that utilizes a positive-drive cog belt and pre-lubricated bearings thereby eliminating the need for oil lubrication of the internal drive mechanism and making the supercharger virtually maintenance free.
Another object is to provide an internal drive mechanism that is relatively quiet in relation to normal engine noise.
Yet another object is to provide an internal drive mechanism that incorporates stabilizing components to reduce tension and stress on the belt.
The present invention relates generally to an improved supercharger or air compressor that advantageously incorporates an internal drive mechanism utilizing a pair of sprockets mounted on parallel input and output shafts respectively and drivingly connected by a taut, endless cog-belt trained around and engagingly running on the two sprockets. More importantly, the present invention relates to several stabilizing components which alone and together serve to stabilize the tension and stress in the belt, thus allowing the belt to be operated at speeds and under loads that otherwise would destroy the belt. One such stabilizing component is the means for evacuating air trapped between the belt and the output sprocket which, at high speeds, adds unnecessary tension to the belt and may even cause the belt to disengage from the output sprocket. Another such stabilizing component is a pair of springs nested against the respective input and output drive shafts to reduce unwanted vibration which may occur during acceleration or especially severe deceleration of the belt.
The input shaft is received within the inner races of pre-lubricated, sealed ball bearings having outer races anchored to the supercharger housing and the output shaft is received within the inner races of double-shielded, pre-lubricated ceramic ball bearings having outer races anchored to the supercharger housing, thereby eliminating the need for oil lubrication. By eliminating oil lubrication, the drive mechanism is made virtually maintenance-free and generates and retains less heat during operation. The reduced heat means that the drive mechanism produces greater air-flow and consequent horsepower.
The cog-belt is a conventional endless belt containing longitudinal tensioning members such as Kevlar(trademark) or black fiberglass, and drives the impeller at speeds up to and exceeding approximately 40,000 revolutions per minute (RPM). At such speeds, belts can be expected to fail, but it was discovered that the ceramic bearings for the output shaft, the springs reducing vibration in the respective input and output shafts, and the air ducts incorporated into the output shaft each individually and in cooperation function as stabilizing components contributing to the operational life of the belt for virtually maintenance-free high-speed, operation.
In addition, an idler is incorporated into the internal drive mechanism to engage the belt. While conventional wisdom suggests that the idler should be placed to engage the portion of the belt returning from the drive or input shaft, the present invention incorporates the idler to engage the portion of the belt returning from the driven or output shaft. The idler stabilizes the belt during deceleration to prevent additional wear to the belt during rapid and uncontrolled deceleration that can occur under normal stop-and-go traffic conditions. With the idler in its unusual location, the output shaft functions as the drive shaft during deceleration when the idler is needed.